Passing Distance - Bike Lanes vs. Wide Outside Lanes

One of the most common arguments in bicycle transportation circles stems from
the disagreement over whether bike lanes or wide outside lanes provide "better
passing distance". Foresterites claim that wide outside lanes are better
for a variety of reasons; bike lane advocates come back with the "dedicated
space" argument; which Foresterites then attempt to rebut by saying passing
distance is "better" in wide curb lanes.

I have direct experience in this matter: my commutes to work generally take
me along Shoal Creek Boulevard in north central Austin; which had fairly wide
(6'?) bike lanes for several years; and then very wide (19') curb lanes for
several more years. I found that a typical 10-pass scenario would go something
like the table below. The "distance" given is from car's mirror to
where I was riding in approximate center of bike lane.

Passing distance on Shoal Creek Boulevard with Bike Lane

Passing distance on Shoal Creek Boulevard with Wide Outside
Lane

1

3.5 ft

With minor fluctuation, the typical pass
with the bike lane consisted of the driver giving about half a foot
of distance between their right mirror and the bike lane stripe; thus
providing approximately the same passing space every time. Why does
this happen? Motorists are conditioned in other traffic interactions
to respect lane stripes.

2

3.5 ft

3

3.5 ft

4

3.5 ft

5

3.5 ft

6

3.5 ft

7

3.5 ft

8

3.5 ft

9

3.5 ft

10

3.5 ft

1

5 ft

Some motorists (perhaps even a majority)
provide better passing distance in the wide outside lane scenario
because they are thinking about how much space to give, rather than
letting the lane stripe decide for them.

2

5 ft

3

5 ft

4

5 ft

5

5 ft

6

5 ft

7

4 ft

8

3 ft

9

2 ft

On the other hand, some other motorists provide considerably
less passing space without the lane stripe to guide them (some from
ignorance; others from antipathy towards cyclists riding in "their
lane").

10

1 ft

Average passing distance from centerline of my bike: 3.5 ft

Average passing distance from centerline of my bike: 4.0 ft

10th percentile passing distance: 3.5 ft

10th percentile passing distance: 1 ft

In this dataset, the 30th percentile passing distance for wide outside lanes
was worse than for bike lanes; meaning that 3 out of 10 times, the passing distance
could be expected to be less for wide outside lanes than it was for bike lanes.
(Or, to turn it around, 7 out of 10 times, the passing distance in wide outside
lanes would be better than in bike lanes).

Despite the fact that this dataset shows a superior passing distance in 7 out
of 10 cases for wide outside lanes, I would choose the bike lane over the wide
outside lane in this scenario. I submit that the deciding factor for cyclists,
if they are thinking rationally, should not be the average passing distance;
since most motorists, whatever the facility, do a fairly good job of providing
adequate passing distance. The deciding factor should be the likelihood that
motorists who, because they either don't know or don't care, don't provide adequate
passing distance. Clearly, in my experience, although average passing distance
can be higher in a wide outside lane scenario, the minimum passing distance
can at the same time be a lot lower. In this dataset, for instance, I'd argue
that the 2 ft and 1 ft passes were close enough to be dangerous (given my width).